Due to their lightweight, as well as their reduced size and complexity, shape memory alloy (SMA) manipulators or actuators provide numerous advantages over traditional motor-based actuators. For example, SMA actuators have been used in a variety of robotic applications, such as in the case of micro-manipulators, pumps, bio-inspired inchworms, biomimetic fish, and robotic octopi, for example. In addition, SMA actuators have been utilized in robotic hands, whereby wires formed of SMA are attached across the joints of the robotic fingers to control their movement. In such robotic hand applications, the fingers of the robotic hand are actuated by heating the SMA wire, which results in the flexion or the extension of the finger joint. In addition, some robotic hands are designed to be actuated by SMA wires via a finger tendon drive system, whereby the SMA wires are positioned in series with the linear springs or through segmented binary control. SMA actuators have also been used in conjunction with DC (direct current) motors for hybrid actuation of an artificial finger and a surgical manipulator.
In order to control an SMA actuator, it must be heated in order to cause it to transition from an initial “untrained” shape (martensite phase) to a second predetermined or “trained” shape (austenite phase), and then subsequently cooled so that the SMA actuator returns back to its initial shape (martensite phase). During the heating phase, SMA actuators have a fast response time, whereby they can reach their austenite phase or their “trained” shape very rapidly. However, one problem with SMA-based robotic hands is that the SMA actuators require a lengthy amount of time to cool down so that the actuator can return to its initial “untrained” shape in its martensite phase. This slow transition time between the “memory” or “trained” shape in its austenite phase, back to the “untrained” shape in its martensite phase results in a low-bandwidth system, which limits the use of the SMA actuators in various applications, such as robotics, such as in prosthetics limbs and hands.
Due to the low-bandwidth operation of the SMA actuators in robotic or prosthetic devices, several attempts have been made to overcome this obstacle. For example, a differential pulley system has been developed, which uses antagonistic SMA wires, whereby opposing SMA wires drive the joint in either direction. This increases the response speed of the SMA robotic system, as compared to conventional SMA robotic systems that utilize a return spring to facilitate the movement of the SMA actuator from the memory/trained shape of its autenite phase, back to its initial shape of its martensite phase. However, while such differential pulley-based robotic systems have improved operating performance, they are complex, and as a result, require frequent maintenance and repair, which is undesirable. However, while such antagonistic SMA robotic systems have improved response speed, such systems could achieve further improvements in operating performance if the SMA wires used thereby were cooled in an efficient manner.
Therefore, there is a need for a manipulator that uses antagonistically controlled shape memory alloy (SMA) actuators to control its movement. There is also a need for a manipulator that uses antagonistically controlled shape memory alloy (SMA) actuators, which are cooled by liquid such as water to increase the speed of the manipulator to move from its austenite phase to its martensite phase. In addition, there is a need for an antagonistic shape memory alloy (SMA) manipulator or actuator for a prosthesis, such as prosthetic finger of a prosthetic hand, which has an enhanced cooling system. Additionally, there is a need for an antagonistic SMA actuator for a prosthesis, such as a prosthetic finger, which has individual cavities that are configured to carry antagonistically orientated SMA actuators therein, whereby one actuator is trained to have a flexion shape in its austenite phase and the other actuator is trained to have an extension shape in its austenite phase. Furthermore, there is a need for an antagonistic SMA actuator for a prosthetic finger, which includes ports to allow water to enter and exit prosthetic finger, so as to cool the SMA actuator, when the prosthetic finger is submerged in water.